$ { {5} \times \left[\begin{array}{rrr}{1} & {-1} & {3} \\ {1} & {4} & {2}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{5}\times{1} & {5}\times{-1} & {5}\times{3} \\ {5}\times{1} & {5}\times{4} & {5}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{5} & {-5} & {15} \\ {5} & {20} & {10}\end{array}\right]}$